1. Field of the Invention
The present invention relates to a waveguide for a microwave device used as a satellite communication transmitter and the like.
2. Description of the Related Art
For example, a satellite communication transmitter as a microwave device is generally provided with a circuit board having a high-frequency circuit thereon. The high-frequency circuit includes an intermediate-frequency amplifier circuit, a local oscillator circuit, a hybrid power-amplifier circuit, and so forth. The circuit board is housed in a metal frame and capped by a cover plate. The intermediate-frequency amplifier circuit amplifies intermediate-frequency input signals to a certain power level. The hybrid power-amplifier circuit includes a frequency mixer as a frequency converter, a band-pass filter, and a power amplifier. The frequency mixer converts frequencies of the intermediate-frequency signals received from the intermediate-frequency amplifier circuit to predetermined high-frequencies in accordance with local oscillation signals received from the local oscillator circuit. Then, the band-pass filter allows the signals to pass through only when the converted frequencies lie in a predetermined frequency range. Subsequently, the power amplifier amplifies the signals passing through the band-pass filter to a sufficient degree of amplification so as to transmit the signals.
In such a satellite communication transmitter, the high frequency signals amplified by the hybrid power-amplifier circuit are transmitted into a waveguide via a probe, and then are emitted into air via a horn at an end of the waveguide. A known structure of the waveguide is such that the end of the probe protrudes from a side surface of the frame and also the waveguide, which is integrally molded by, e.g., aluminum die-casting, is fixed to the side surface of the frame in order that the end of the probe is inserted in the waveguide.
However, in the aforementioned known art, fixing the integrally molded waveguide to the frame of the microwave device substantially reduces the space for mounting components of the device due to the required waveguide length, and also bringing the end of the opening of the waveguide into line with the probe substantially limits the layout design freedom of the components including the waveguide.
In view of the aforementioned known art, it is an object of the present invention to provide a waveguide for a microwave device, which provides sufficient space for mounting device components and enhanced layout design freedom for the components.
To this end, a waveguide for a microwave device according to the present invention comprises a frame for housing a high-frequency circuit therein, and a lid attached to a sidewall of the frame, wherein at least one of the frame and the lid has a waveguide groove formed therein and extending along the mating surface between the frame and the lid.
In the waveguide configured as described above, the lid is attached to the sidewall of the frame and covers the waveguide groove formed at least one of the frame and the lid so as to function as a waveguide, thereby providing sufficient space for device components and improved layout design freedom for the components.
In the above configuration, the frame may comprise a main casing housing a first circuit board and a sub-casing housing a second circuit board, and the second circuit board may have a probe provided thereon such that the probe protrudes into the waveguide groove. This arrangement makes sure to shield circuit components including a probe mounted on the second circuit board and other circuits components mounted on the first circuit board.
Further, in the above configuration, the lid may have a projected flange formed thereon so as to serve as a fixing surface for a mating waveguide, and the flange may have a waveguide through-hole therein so that the waveguide groove is in continuous connection with the waveguide through-hole via an inclined plane formed at an end of the waveguide groove. This arrangement reduces the proportion of the surface area of the flange relative to the overall outer surface area of the lid, and makes it easy to obtain the flat end surface of the flange, thus allowing the mating waveguide to be accurately mounted on the end surface of the flange of the lid.
Furthermore, in the above configuration, the sub-casing is preferably arranged inside the four sidewalls of the main casing and the main casing preferably has a through-hole formed in the sidewall to which the lid is attached so that the probe penetrates through the through-hole.
Alternatively, the main casing may have a cut-out formed in the sidewall to which the lid is attached and the sub-casing arranged inside the main casing may have a sidewall which is exposed at the cut-out. In this arrangement, both the main casing and the sub-casing preferably have waveguide grooves formed in the respective sidewalls, and the lid preferably has a flat surface to cover the waveguide grooves.